Division of Bio-Information Engineering, Faculty of Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
Peptides. 2009 Oct;30(10):1901-8. doi: 10.1016/j.peptides.2009.07.014. Epub 2009 Jul 29.
Ghrelin, a gut and brain peptide, is a potent stimulant for growth hormone (GH) secretion and feeding. Recent studies further show a critical role of ghrelin in the regulation of sleep-wakefulness. Laterodorsal tegmental nucleus (LDT), that regulates waking and rapid eye movement (REM) sleep, expresses GH secretagogue receptors (GHS-Rs). Thus, the present study was carried out to examine electrophysiological effects of ghrelin on LDT neurons using rat brainstem slices, and to determine the ionic mechanism involved. Whole cell recording revealed that ghrelin depolarizes LDT neurons dose-dependently in normal artificial cerebrospinal fluid (ACSF). The depolarization persisted in tetrodotoxin-containing ACSF (TTX ACSF), and is partially blocked by the application of [D-Lys3]-GHRP-6, a selective antagonist for GHS-Rs. Membrane resistance during the ghrelin-induced depolarization increased by about 18% than that before the depolarization. In addition, the ghrelin-induced depolarization was drastically reduced in high-K+ TTX ACSF with a K+ concentration of 13.25 mM. Reversal potentials obtained from I-V curves before and during the depolarization were about -83 mV, close to the equilibrium potential of the K+ channel. Most of the LDT neurons recorded were characterized by an A-current or both the A-current and a low threshold Ca2+ spike, and they were predominantly cholinergic. These results indicate that ghrelin depolarizes LDT neurons postsynaptically and dose-dependently via GHS-Rs, and that the ionic mechanisms underlying the ghrelin-induced depolarization include a decrease of K+ conductance. The results also suggest that LDT neurons are implicated in the cellular processes through which ghrelin participates in the regulation of sleep-wakefulness.
生长激素释放肽（ghrelin）是一种肠脑肽，对生长激素（GH）的分泌和摄食有很强的刺激作用。最近的研究进一步表明，ghrelin 在调节睡眠-觉醒中起着关键作用。调节觉醒和快速眼动（REM）睡眠的外侧缰核（LDT）表达生长激素促分泌素受体（GHS-Rs）。因此，本研究使用大鼠脑片，观察了 ghrelin 对 LDT 神经元的电生理作用，并确定了所涉及的离子机制。全细胞膜片钳记录显示，ghrelin 在正常人工脑脊液（ACSF）中剂量依赖性地使 LDT 神经元去极化。这种去极化在含河豚毒素的 ACSF（TTX ACSF）中持续存在，并且部分被 GHS-Rs 的选择性拮抗剂[D-Lys3]-GHRP-6 阻断。与去极化前相比，ghrelin 诱导的去极化期间的膜电阻增加了约 18%。此外，在高钾 TTX ACSF（钾浓度为 13.25mM）中，ghrelin 诱导的去极化大大减少。在去极化前后的 I-V 曲线中获得的反转电位约为-83mV，接近钾通道的平衡电位。记录的大多数 LDT 神经元的特征是 A 电流或 A 电流和低阈值 Ca2+ 峰两者之一，它们主要是胆碱能的。这些结果表明，ghrelin 通过 GHS-Rs 突触后和剂量依赖性地使 LDT 神经元去极化，ghrelin 诱导的去极化的离子机制包括钾电导的降低。结果还表明，LDT 神经元参与了 ghrelin 参与调节睡眠-觉醒的细胞过程。
